Perpendicular magnetic recording (PMR) has become the mainstream technology for disk drive applications beyond 200 Gbit/in2, replacing longitudinal magnetic recording (LMR) devices. The demand for improved performance drives the need for a higher areal density which in turn calls for a continuous reduction in transducer size. A PMR head which combines the features of a single pole writer and a double layered media (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density. Typically, a dual purpose transducer is preferred in which the write head (PMR function) is combined with a read head function in the same structure to form a merged read/write head. The read head may be based on a TMR element in which a tunnel barrier layer separates two ferromagnetic (FM) layers where a first FM layer has a fixed magnetization direction and the second FM layer has a magnetic moment that is free to rotate from a direction parallel to that of the “fixed” layer to a direction anti-parallel to the fixed layer and thereby establish two different magnetic states generally referred to as a “0” state and a “1” state. The read process determines which of the two states the TMR element has been written to.
It is well known that the magnetic storage density increases as the gap (flying or fly height) between the magnetic media and the merged read/write head decreases. In other words, the so-called air bearing surface (ABS) or exposed plane of the merged read/write head that includes the write pole tip is brought closer to the magnetic media to enhance performance. However, due to non-uniformity in production, the fly height may vary from one slider to the next. Therefore, a low fly height may easily cause one or both of the read head and write head to contact the magnetic media which leads to poor reliability and a damaged device. Furthermore, the heat generated when a current is applied to the coils in a write head tends to cause a thermal expansion of the write pole toward the magnetic media. If there is only one heater to control fly height between read/write head and magnetic media, then the read head may have a lower protrusion into the read gap than desired which causes a loss in read sensitivity. Gamma ratio is a critical parameter used to characterize a read/write head because it describes the relationship of mechanical minfly point to magnetic spacing. A lower gamma ratio means a larger gap between the mechanical minfly point and the reader location. An important head design objective is to achieve a gamma as close as possible to 1 which is ideal for tribology and magnetic performance since it keeps the gap between reader and minfly point at a constant value independent of DFH power (actuation). From a drive reliability point, the reader should not be at the minfly point which is the mechanically closet part of the head to the disk because the read head sensor is too sensitive towards mechanical impact. Ideally, the read head should be recessed from the minfly point by at least 0.5 nm.
A popular design used to control fly height is to position a dynamic fly heater (DFH) opposite the read head or the main pole layer in the write head with respect to the ABS. When the heater is activated, thermal expansion of nearby layers including the write pole in the write head effectively pushes the write pole tip closer to the magnetic media. Likewise, heating of layers in the vicinity of the sensor in the read head causes thermal expansion which results in a read head protrusion toward the magnetic media and thereby reduces the fly height.
One example of a thermal control mechanism is found in U.S. Pat. No. 7,068,468 where a read head element and a first heater are sandwiched between a lower flexible layer and a middle flexible layer, and a write head element and a second heater are sandwiched between the middle flexible layer and an upper flexible layer. The three flexible layers participate in the thermal expansion process and the two heaters are independently operated such that only one may be activated at a certain time.
In U.S. Pat. No. 7,113,369, leads for an inductive electromagnetic transducer and a magnetoresistive device are separated from each other by the leads of a heater so that crosstalk to the lead of the magnetoresistive device can be prevented when a current is supplied to the lead of the inductive electromagnetic transducer.
U.S. Pat. No. 7,203,035 discloses a heater formed in an overcoat layer above a magnetic write head. The heater has a heating part with a predetermined sheet resistance and a lead part which is connected in series to the heating part and has a sheet resistance lower than that of the heating part.
U.S. Patent Application No. 2006/0077591 describes a heat sink element used to prevent melting of the heat control layer in the heater element. The heat from the heat sink element flows selectively toward upper and lower shield layers and the magnetic pole layer and thereby reduces the amount of heat that is directed in other directions.
U.S. Pat. No. 6,999,265 teaches a first fly height adjustment using an electromechanical control mechanism and a second fly height adjustment with a thermal control mechanism.
Unfortunately, heater elements in the prior art tend to be located a substantial distance from the write pole tip and read head sensor element at the ABS. Thus, there is a significant actuation time for the heater elements to activate and for thermal energy to be transferred to the write pole tip and read head sensor along the ABS and thereby reduce the fly height. As a result, improvements in read time and write time are limited by a substantial actuation time. Furthermore, the heater elements heat a substantial part of the write head, read head, and surrounding layers so that considerable power consumption is required. A novel heater configuration is needed to allow an in-situ adjustment of gamma ratio that improves reader reliability, and to achieve short actuation times and low power consumption.